Multilateral well drilling and production, where a wellbore may have multiple wells branching off of a common wellbore have become increasingly important as a way to both maximize drilling efficiency and to minimize the wellsite footprint on the surface.
In the past a main wellbore was drilled, once completed, a packer was set in the well at a location in the well corresponding to the location that the window for the first branch or sidetrack well was desired. Once the packer was set the tool string was removed from the well and a measuring device was run into the well to determine the orientation of the keyslot or orientation device on top of the packer. After determining the orientation of the keyslot the measuring device was removed from the well and the whipstock/mill assembly was run into the well. A key on the bottom of the whipstock/mill assembly was preset on the surface, based upon the data gathered by the measuring device, so that the whipstock/mill assembly would be pointing in the desired direction when the whipstock/mill assembly was landed on the packer. The whipstock/mill assembly may then be used to cut a window into the casing so that a second well or branch may be drilled from the window and produced through the common wellbore.
In order to improve the efficiency of the drilling process operators streamlined the sidetracking operation by running the packer, the measuring device, and the whipstock/mill assembly into the well in a single operation. The typical packer used in single trip sidetrack operations is a hydraulically actuated packer.
Typically, the single trip whipstock/mill assembly has the packer or anchor attached beneath the whipstock/mill assembly and the measuring device, usually a measuring while drilling or MWD tool, is attached above the whipstock/mill assembly. The MWD tool uses pressure pulses to send a signal to the surface that notifies the operator of the orientation and direction of the MWD tool and thus the orientation of the whipstock/mill assembly. To send the signal the MWD tool requires power to sense its direction and orientation as well as to send the signal to the surface. The power is provided by the drilling fluid. A typical MWD tool requires a flow rate from between 200 gallons per minute or GPM to about 400 GPM.
One of the difficulties in utilizing a hydraulically actuated packer in the whipstock/mill assembly is the complexity of the typical packers currently in use. The present invention provides significant advantages in reliability due to its simplicity.